Hi,
I have already solved my problem.
I am going to try to explain what I did.
1 - Downloaded, compiled and installed xfree86 4.4.0
2 - Discovered all the packages .deb made from xfree86 sources ->
http://ftp.debian.org/debian/pool/main/x/xfree86/
3 - With grep and a script, I created automatically one file for each
deb package (equivalent to do lots of times: equivs-control name):
------------------------------
Section: x11
Priority: optional
Standards-Version: 4.4.0
Package: xlibs
Version: 4.4.0
Maintainer: XX <XX@fe.up.pt>
Provides: xlibs
------------------------------
to be used with equivs.
4 - I created a script that for all packages made
equivs-build name
and then :
dpkg -i name_4.4.0_all.deb
After this I could install xemacs21 with apt-get install, without having
any problems with dependencies. Note that apt-get did not install the
packages related with xfree86.
Therefore, I installed the sources of the xfree86 4.4.0 and "told" to
apt that all packages related with xfree86 were installed.
--
Ricardo Lima

Great job! So to show the details of what you did for just one set of
<name> debs, e.g. xlibs: